Perhaps an SSR for your application is unavailable or too costly. For a specialized solution, the additional devices outlined present further options.Ī thoughtful engineer occasionally reevaluates their chosen components and methods. Choose a transistor for smaller loads, when power consumption is important, or if you need to switch something millions or billions of times. It's a marvel of miniaturization.įor very high or unknown loads, a relay is your best and most practical option. Computer Chip: You may not want to develop your own computing device from scratch, but it’s worth noting that these chips pack billions of transistors into a package that can easily fit in your palm.TRIAC: Short for “triode for alternating current,” the TRIAC is a solid-state device that allows current to flow in either direction through two main terminals.These devices generally feature only NO contacts. Contactor: Contactor relays are optimized for switching large currents, such as starting electrical motors.These devices are silent, switch in a millisecond or less, and are more reliable than conventional relays. The LED activates a light-activated MOSFET that controls the load. Solid-State Relay: A sort of hybrid between a conventional relay and a transistor, these relays switch a load using an LED activated by the control circuitry.Typical transistors and relays have virtually limitless applications, but these specialized solutions perform similar tasks. You’ll need to properly specify your transistor, whereas relays can tolerate a wide range of power types.Designers need to know more about the switched device than when using a relay. You can use a transistor to allow one signal to switch a larger load, but it’s not entirely independent.Transistors are silent, and don’t indicate whether they are activated.They’re much smaller than the equivalent relay.Transistors can behave as analog devices, allowing for signal amplification.Switching ranges are typically in the nanosecond (10 -9 second) range, many orders of magnitude faster than the equivalent relay. Here are eight specific characteristics of transistors, as opposed to relays: Instead, when positive voltage is present, the transistor varies the conductivity of the transistor’s material. Transistors allow current to flow between the collector and emitter, as opposed to an on/off switch. Latching relays are available that require power only to turn on and off.įinally, relays are usually much larger than transistors, and they are electromagnetic devices, so they can cause electromagnetic flux (EMF) interference. Relays also consume a relatively large amount of current in the on-state. Switching is much slower than with transistors, and contacts may “bounce,” leading to a signal that flutters on and off momentarily when you operate the switch. Others feature a bypass/test button or a switch to actuate the relay manually. Some relays allow you visually observe their state. This has its advantages but may present a disadvantage when noise is an issue. Relays emit an audible clicking noise when turned on or off. You can use both NO and NC simultaneously, if needed. Most relays feature a NO (normally open) and NC (normally closed) contact, allowing you to either close the circuit when power is applied (NO) or open the circuit (NC). From an electrical point of view, a closed relay is virtually identical to an unbroken wire. Relays experience very low resistance.Relays can handle alternating current (AC) or direct current (DC) loads.Relays can switch loads regardless of the device’s internal circuitry.Relays handle much higher current and voltage loads.Here are five of their biggest differences: Relays are distinct from transistors in a few key ways. Typically, they use an electromagnet reed switch to allow a small electric signal to switch much higher voltages. Relays are a time-tested technology, and they physically switch contacts as if you were throwing a switch yourself. To evaluate which will work best for your application, it’s important to understand the details of each device’s characteristics. Depending on your experience and industry, you may default to one or the other, but each device has its own advantages and disadvantages. Nominally, both devices do the same job-they switch the flow of current on and off-but they use very different methods. The engineering world knows this struggle well, and transistors and relays are a perfect example.
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